The Story mode of The Metronomicon is split into a total of 5 areas, called Dungeons. There is also a standalone DLC Dungeon. Each Dungeon (with the sole exception of the DLC Dungeon) has a total of 10 songs/levels, as well as 4 sidequests total.
When you enter a Dungeon for the first time, you can only access the first 7 songs. As you gradually continue to survive more levels and defeat more minibosses in each level, the remaining songs and the sidequests will become accessible. The sidequests will vary in scope, but there will always be a sidequest for the fastest timed boss kill in each Dungeon.
- For the first three sidequests, simply survive the song that has an associated sidequest.
- To unlock the fourth sidequest, the fastest timed boss kill sidequest, defeat all the minibosses in the dungeon, plus the boss.
- The song list in each dungeon will tell you which four songs in a given dungeon has an associated sidequest.
- To unlock the first hidden song, beat 3 minibosses in the dungeon.
- To unlock the second hidden song, beat 6 minibosses.
- Simply survive any 6 songs in order to unlock the boss song.